Coffee Drinking May Help Protect Against Type 2 Diabetes

October 9, 2008 — Regular consumption of coffee and potentially black tea, but not green tea, is associated with a lower risk for type 2 diabetes mellitus in Singaporean Chinese men and women, according to the results of a study reported in the October issue of the American Journal of Clinical Nutrition.

"Increasing coffee intake was inversely associated with risk of type 2 diabetes in populations of European descent; however, data from high-risk Asian populations are lacking as are data on tea intake in general," write Andrew O. Odegaard, from the University of Minnesota in Minneapolis, and colleagues. "We investigated the prospective associations between intakes of coffee, black tea, and green tea with the risk of type 2 diabetes in Singaporean Chinese men and women."

The study cohort, from the Singapore Chinese Health Study, consisted of 36,908 men and women aged 45 to 74 years between 1993 and 1998, who underwent evaluation of multiple diet and lifestyle measures and who were then followed up between 1999 and 2004. To examine the association of baseline coffee and tea intakes with incident type 2 diabetes during follow-up, the investigators used Cox regression models, with adjustment for several possible confounding or mediating variables.

Compared with participants who reported not drinking coffee daily, those who reported drinking 4 or more cups of coffee daily had a 30% reduction in the risk for diabetes (relative risk [RR], 0.70; 95% confidence interval [CI], 0.53 - 0.93). Compared with participants who reported not drinking black tea daily, those who reported drinking 1 or more cups of black tea daily had a suggestive 14% reduction in the risk for diabetes (RR, 0.86; 95% CI, 0.74 - 1.00). There was no apparent association with green tea.

"Regular consumption of coffee and potentially black tea, but not green tea, is associated with lower risk of type 2 diabetes in Asian men and women in Singapore," the study authors write.
Limitations of this study include potential misclassification of the exposures because of poor self-report, biases, and other errors; possible residual confounding; and results for black and green tea consumption applying only to a smaller range of intake vs coffee.

"The associations we observed are noteworthy because they provide evidence that the coffee findings in other prospective cohort studies are not likely artifacts of the reported dietary patterns, nor are they likely to be explained by residual confounding," the study authors conclude. "Given the high consumption of coffee and tea worldwide and the growing type 2 diabetes epidemic, especially in Asia, these findings convey a potential high significance for public health. However, it is too early to recommend increasing coffee and tea consumption until there is more thorough data from clinical trials related to the topic, with respect to not only the possible benefits but possible side effects or harm as well."

The National Cancer Institute supported this study. The study authors have disclosed no relevant financial relationships.
Am J Clin Nutr. 2008;88:979-985.